patch "ihex: Simplify next record offset calculation" added to driver-core-next

patch "ihex: Simplify next record offset calculation" added to driver-core-next

[gregkh]

This is a note to let you know that I've just added the patch titled

    ihex: Simplify next record offset calculation

to my driver-core git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git
in the driver-core-next branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release
during the merge window.

If you have any questions about this process, please let me know.


From 9fb4ab4d3dd665a62da9c176a89e7c7feaf5d9e4 Mon Sep 17 00:00:00 2001
From: Andrey Smirnov <andrew.smirnov@gmail.com>
Date: Thu, 20 Dec 2018 23:28:39 -0800
Subject: ihex: Simplify next record offset calculation

Next record calucaltion can be reduced to a much more tivial ALIGN
operation as follows:

1. Splitting 5 into 2 + 3 we get

   next = ((be16_to_cpu(rec->len) + 2 + 3) & ~3) - 2            (1)

2. Using ALIGN macro we reduce (1) to:

   ALIGN(be16_to_cpu(rec->len) + 2, 4) - 2                      (2)

3. Subsituting 'next' in original next record calucation we get:

   (void *)&rec->data[ALIGN(be16_to_cpu(rec->len) + 2, 4) - 2]  (3)

4. Converting array index to pointer arithmetic we convert (3) into:

   (void *)rec + sizeof(*rec) +
   	 ALIGN(be16_to_cpu(rec->len) + 2, 4) - 2		(4)

5. Subsituting sizeof(*rec) with its value, 6, and substracting 2,
   in (4) we get:

   (void *)rec + ALIGN(be16_to_cpu(rec->len) + 2, 4) + 4        (5)

6. Since ALIGN(X, 4) + 4 == ALIGN(X + 4, 4), (5) can be converted to:

   (void *)rec + ALIGN(be16_to_cpu(rec->len) + 6, 4)            (6)

5. Subsituting 6 in (6) to sizeof(*rec) we get:

   (void *)rec + ALIGN(be16_to_cpu(rec->len) + sizeof(*rec), 4) (7)

Using expression (7) should make it more clear that next record is
located by adding full size of the current record (payload + auxiliary
data) aligned to 4 bytes, to the location of the current one. No
functional change intended.

Cc: Chris Healy <cphealy@gmail.com>
Cc: Kyle McMartin <kyle@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/linux/ihex.h | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/linux/ihex.h b/include/linux/ihex.h
index 9130f307a420..98cb5ce0b0a0 100644
--- a/include/linux/ihex.h
+++ b/include/linux/ihex.h
@@ -21,14 +21,18 @@ struct ihex_binrec {
 	uint8_t data[0];
 } __attribute__((packed));
 
+static inline uint16_t ihex_binrec_size(const struct ihex_binrec *p)
+{
+	return be16_to_cpu(p->len) + sizeof(*p);
+}
+
 /* Find the next record, taking into account the 4-byte alignment */
 static inline const struct ihex_binrec *
 __ihex_next_binrec(const struct ihex_binrec *rec)
 {
-	int next = ((be16_to_cpu(rec->len) + 5) & ~3) - 2;
-	rec = (void *)&rec->data[next];
+	const void *p = rec;
 
-	return rec;
+	return p + ALIGN(ihex_binrec_size(rec), 4);
 }
 
 static inline const struct ihex_binrec *
-- 
2.20.1